You can have the clerk of the court issue a Summons on Cross-Complaint now. It is not a problem. The cross-complaint is still deemed filed from the date of the ruling. The Summons on Cross-Complaint is issued on the date you submit it to the clerk to be issued.
Other than parties who have already appeared in the lawsuit (such as the plaintiff), the Summons on Cross-Complaint AND Cross-Complaint must be personally served.
However, parties who have already appeared can be served by mail by serving their counsel of record.
Frank W. Chen has been licensed to practice law in California since 1988. The information presented here is general in nature and is not intended, nor should be construed, as legal advice for a particular case. This Avvo.com posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, please consult with your own attorney.
Without seeing the original complaint and your cross-complaint, it's not possible to tell you with certainty what to do.
There is no problem with getting a summons issued now on the cross-complaint. It isn't 100% clear that you need one. If the only cross-defendants were the plaintiffs, then no summons is needed. In other words the summons (and subsequent service) is needed only if you have added cross-defendants who were previously not plaintiffs or who had not previously appeared in the case.
It may make sense to sit down with an experienced litigator, buy a block of his or her time, and have him or her help you through these procedural questions.